UVs applied in viewport, but not in render
How the issue was resolved:
I was able to fix the issue by giving each hair object a new name. The previous objects were named &quot;RemeshedHair.00X&quot; with &quot;X&quot; being incremented every time I created a new object. After changing the names to &quot;Hair front/Hair side/Hair back&quot; the UVs were able to be applied properly.
My hypothesis on the cause of the issue:
I no longer have a copy of the .blend that contains the issue, so I can't say for certain what happened, but I can guess. It might be possible that this issue was just some bug in the way that blender handles it's internal data structures. It might be the case that the UV map was somehow unlinked from it's object in the portion of the structure where rendering data is stored, and renaming the object caused an update to that portion of the structure, resolving the issue.